In the Magnificat, Mary refers to God as her Savior. According to Roman Catholic doctrine, Mary was born sinless and remained sinless throughout her life.

So, why does Mary refer to God as her Savior if she was sinless (and therefore would not have need of a Savior or even have one).

And Mary said:

“My soul exalts the Lord, And my spirit has rejoiced in God my
Savior. For He has had regard for the humble state of His
bondslave; for behold, from this time on all generations will count me
blessed. For the Mighty One has done great things for me; and holy
is His name. And His mercy is upon generation after generation Toward
those who fear Him. He has done mighty deeds with His arm; He has
scattered those who were proud in the thoughts of their heart. He
has brought down rulers from their thrones, And has exalted those who
were humble. He has filled the hungry with good things; And sent away
the rich empty-handed. He has given help to Israel His servant, In
remembrance of His mercy, As He spoke to our fathers, To Abraham and
his descendants forever.” (Luke 1:46-55)

This question appears to be asking Roman Catholics to defend their faith using the terms and presuppositions of Protestantism, namely that 'sin' is the biggest reason why we need a Savior.
–
DanJan 2 '14 at 16:45

3 Answers
3

According to Catholic Answers, it was because of God's salvation that she was able to be born sinless and remain sinless.

Paraphrasing, God saved her pre-emptively, preventing (or perhaps keeping/preserving) her from sinning in the first place, something no human could do without God's protective saving power. In other words, in Catholic doctrine, she was sinless, but only through the Grace of God. Without the Grace of God and His keeping power, she could not have remained sinless.

Excerpt:

The Catholic Answer

Not a few Protestants are surprised to discover the Catholic Church
actually agrees that Mary was "saved." Indeed, Mary needed a savior!
However, Mary was "saved" from sin in a most sublime manner. She was
given the grace to be "saved" completely from sin so that she never
committed even the slightest transgression. Protestants tend to
emphasize God’s "salvation" almost exclusively to the forgiveness of
sins actually committed. However, Sacred Scripture indicates that
salvation can also refer to man being protected from sinning before
the fact:

I was reluctant to post this answer in view of a good answer posted by @David but thought it would be better if it is clarified a little more.

The essence of original sin consists in the deprivation of sanctifying grace, and its stain is a corrupt nature. Mary was preserved from these defects by God's grace; from the first instant of her existence she was in the state of sanctifying grace and was free from the corrupt nature that original sin brings. Mary therefore says:

Luke 1:47 and my spirit has begun to rejoice in God my Savior,

Some argue that this indicates that Mary was sinner, since only sinners needs a saviour. But it is not so. Like all other descendants of Adam, she was subject to the necessity of contracting original sin. But by special intervention of God, undertaken at the instant she was conceived, she was preserved from the stain of original sin and its consequences. She was therefore redeemed by the grace of Christ, but in a special way ---by anticipation.

To quote an analogy that I read: Suppose a man falls into a deep pit and someone reaches down to pull him out. The man has been saved from the pit. Now imagine a woman walking along and she is about to topple into the pit, but at the very moment that she is to fall in, someone holds her back and prevents her. She too has been saved from the pit, but in an even better way: She was not simply taken out of the pit; she was spared from getting strained by the mud in the first place. In this way God became her saviour in a special way and hence her exclaim. She has more reason to call God her saviour than we do, because He saved her in an even more glorious manner.

As per New Advent, the formal active essence of original sin was not removed from her soul, as it is removed from others by baptism; it was excluded, it never was in her soul. Simultaneously with the exclusion of sin. The state of original sanctity, innocence, and justice, as opposed to original sin, was conferred upon her, by which gift every stain and fault, all depraved emotions, passions, and debilities, essentially pertaining to original sin, were excluded. But she was not made exempt from the temporal penalties of Adam — from sorrow, bodily infirmities, and death.

Now unto him that is able to keep you from falling, and to present you faultless before the presence of his glory with exceeding joy. To the only wise God our Savior, be glory and majesty, dominion, and power, both now and forever, Amen. Jude 1:24-25 KJV

Mary was saved because her Savior prevented her from falling into sin. "Full of Grace"

Welcome to the site! Thanks for the answer. Typically, a good answer will not just quote Scripture or something else, but will also explain why and how this answers the question. This has the makings of a good answer if you can expand on it a bit more.
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NarnianJan 2 '14 at 16:14